Load control device for controlling a driver for a lighting load

ABSTRACT

If there is an interruption of power to an electrical load while the electrical load is operating at low end, the electrical load may not turn back on when power is restored. This undesired operation may be avoided by detecting the application of power to the electrical load, and automatically increasing the magnitude of a control signal being applied to the electrical load by a sufficient amount for a short period of time after power has been applied. This way, the electrical load may be turned back on to low end, instead of erroneously operating in an electronic off condition.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Provisional U.S. PatentApplication No. 62/398,636, filed Sep. 23, 2016, the disclosure of whichis incorporated herein by reference in its entirety.

BACKGROUND

A lighting source, such as a light-emitting diode (LED) light source, istypically driven by a load regulation device (e.g., such as an LEDdriver) in order to illuminate. A common control method for dimming anLED light source controlled by an LED driver is “zero-to-ten-volt”(0-10V) control, which is sometimes referred to as 1-10V control. A0-10V LED driver receives power from an AC power source, with anexternal mechanical switch typically coupled between the AC power sourceand the 0-10V driver to provide a switched-hot voltage to the driver.Alternatively, the switched-hot voltage may be generated by an externalpower device (e.g., a power pack). The 0-10V driver controls theintensity of the connected LED light source in response to a 0-10Vcontrol signal received from a 0-10V control device (e.g., a 0-10Vcontroller). Often, the 0-10V control device is mounted in an electricalwallbox and comprises an intensity adjustment actuator (e.g., a slidercontrol). The 0-10 V control device regulates the direct-current (DC)voltage level of the 0-10V control signal provided to the driver betweena substantially low voltage (e.g., zero to one volt) to a maximumvoltage (e.g., approximately ten volts) in response to an actuation ofthe intensity adjustment actuator. For example, the 0-10V driver maycontrol the intensity of the LED light source to a low-end intensityL_(LE) (e.g., approximately 0.1%-10%) when the DC voltage level of the0-10V control signal is at the substantially low voltage (e.g., zero toone volt) and to a high-end intensity L_(HE) (e.g., approximately 100%)when the DC voltage level of the 0-10V control signal is at the maximumvoltage (e.g., approximately ten volts).

To turn off the LED light source controlled by the 0-10V driver, poweris removed from the 0-10V driver by, for example, controlling theswitched-hot voltage to zero volts. The 0-10V control device maycomprise a switching circuit for generating the switched-hot voltage.The switching circuit may include, for example, a mechanical air-gapswitch, a relay, and/or a bidirectional semiconductor switch, such as atriac, one or more silicon-controlled rectifiers (SCRs), a field-effecttransistor (FET) in a rectifier bridge, two FETs in anti-seriesconnection, one or more insulated-gate bipolar junction transistors(IGBTs), or any suitable semiconductor switching circuit. In some cases,the 0-10V control device may be powered via the 0-10V control wires, forexample, by drawing current from the 0-10V driver. Prior art 0-10Vdrivers typically source between 1-2 milliamperes of current, which the0-10V control device may use to power itself.

Some 0-10 V drivers may be responsive to occupancy sensors, vacancysensors, and/or daylight sensors. If the switched-hot voltage iscontrolled to zero volts to turn off the LED light source (e.g., byopening the switching circuit of the 0-10V control device or the powerpack), the 0-10V driver will then be unpowered and unable to respond tothe occupancy sensors, vacancy sensors, and/or daylight sensors.

Rather than removing power from an 0-10V driver to turn off the LEDlight source, the 0-10V driver may be controlled to an electronic off(e.g., standby) state in which the 0-10V driver remains powered, butturns off the LED light source. The 0-10V driver may be configured tochange between an on state and the electronic off state in response tothe 0-10V signal (e.g., using hysteresis). For example, during the onstate, the 0-10V control device may be configured to adjust the DCvoltage level of the 0-10V control signal between a minimum level (e.g.,approximately 0.61-1.00 volts) and a maximum level (e.g., approximatelyten volts) to adjust the intensity of the LED light source between thelow-end intensity L_(LE) and the high-end intensity L_(HE),respectively. To control the 0-10V driver into the electronic off state,the 0-10V control device may be configured to adjust the DC voltagelevel of the 0-10V control signal to a standby level. For example, the0-10V driver may be configured to change to the electronic off statewhen the DC voltage level of the 0-10V control signal drops below afalling threshold (e.g., approximately 0.6 V). The 0-10V driver may beconfigured to return to the on state (e.g., to turn on) when the DCvoltage level of the 0-10V control signal rises above a rising threshold(e.g., approximately 1.0 V), after which the 0-10V driver may adjust theintensity of the LED light source between the low-end intensity L_(LE)and the high-end intensity L_(HE) as the 0-10V control signal rangesbetween the minimum level and the maximum level.

Since the falling threshold may be approximately 0.6 V, the DC voltagelevel of 0-10V control signal may be as low as 0.61 V when the 0-10Vdriver is being controlled to the low-end intensity L_(LE). This meansthat the DC voltage level of 0-10V control signal at the low-endintensity L_(LE) may be between the rising threshold and the fallingthreshold. If there is a momentary interruption of the power, such as apower outage or a manual switch-off of power to the 0-10V driver whenthe 0-10V driver is in the on state, and the DC voltage level of the0-10V control signal is between the rising threshold and the fallingthreshold, the 0-10V driver may not turn back on when power is restored(e.g., re-applied) because the DC voltage level of 0-10V control signalwill not be above the rising threshold. It is undesirable for a lightingload that is on to not turn back after a momentary power interruption.

SUMMARY

As described herein, a load control device for controlling an amount ofpower delivered to a lighting load may comprise a communication circuitconfigured to generate a control signal for controlling the amount ofpower delivered to the lighting load. The control signal may cause thelighting load to be turned on when the magnitude of the control signalrises above a threshold. The load control device may also comprise acontrol circuit configured to control the communication circuit toadjust the magnitude of the control signal so as to adjust an intensityof the lighting load between a low-end intensity and a high-endintensity. The magnitude of the control signal may be less than thethreshold when the intensity of the lighting load is being controlled tothe low-end intensity. When power has been applied to the lighting load,the control circuit may be configured to determine that a desiredmagnitude of the control signal is below the threshold, and increase themagnitude of the control signal to be equal to or greater than thethreshold before decreasing the magnitude of the control signal to thedesired magnitude.

The load control device described herein may include an intensityadjustment actuator and a potentiometer circuit responsive to theintensity adjustment actuator for determining the desired magnitude ofthe control signal. The load control device may further include a sensecircuit configured to provide an indication of when power has beenapplied to the lighting load. Once power has been applied to thelighting load and the magnitude of the control signal is set to be equalto or greater than the threshold, the control circuit of the loadcontrol device may cause the magnitude of the control signal to bedecreased to the desired magnitude over a first period of time. Thecontrol circuit may maintain the magnitude of the control signalconstant at a level equal to or greater than the threshold for a secondperiod of time before decreasing the magnitude of the control signal tothe desired magnitude over the first period of time.

Other features and advantages of the present invention will becomeapparent from the following description of the invention that refers tothe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a simplified block diagram of an example 0-10V load controldevice.

FIG. 2 is a simplified flowchart of a voltage sense procedure that maybe executed by a microprocessor of a control circuit of the load controldevice of FIG. 1.

FIG. 3 is a simplified diagram of example waveforms illustrating theoperation of the load control device during the voltage sense procedureof FIG. 2.

FIG. 4 is a simplified block diagram of another example 0-10V loadcontrol device.

FIG. 5 is a simplified diagram of example waveforms illustrating theoperation of a bump-up circuit of the load control device of FIG. 4.

DETAILED DESCRIPTION

Described herein are examples of a load control system for controllingthe amount of power delivered to an electrical load, such as a lightingload, and more particularly, of a wall-mounted load control device forcontrolling a load regulation device, such as an LED driver for an LEDlight source, via a control signal, such as a 0-10V control signal.

FIG. 1 is a simplified block diagram of an example 0-10V load controldevice 100. The load control device 100 may comprise a hot terminal Hadapted to be coupled to an AC power source 102 and a switched hotterminal SH adapted to be coupled to an electrical load. The electricalload may comprise a load regulation circuit for driving a lighting load,such as an LED driver 104 for controlling an LED light source 106. In anexample, the load control device 100 may comprise a neutral terminal Nadapted to be coupled to the neutral side of the AC power source 102. Inanother example, the load control device 100 may not require connectionto the neutral side of the AC power source 102 via the neutral terminalN (e.g., the load control device may be a “two-wire” load controldevice).

The load control device 100 may comprise first and second controlterminals C1, C2 adapted to be coupled to the LED driver 104 via acontrol wiring 108. The LED driver 104 may be configured to control thepower delivered to the LED light source 106, and thus the intensity ofthe LED light source 106, in response to a direct-current (DC) controlsignal V_(CS) received from the load control device 100 via the controlwiring 108. For example, the LED driver 104 may be configured to turnthe LED light source 106 on and off, and/or to adjust the intensity ofthe LED light source 106 between a low-end (e.g., minimum) intensityL_(LE) and a high-end (e.g., maximum) intensity L_(HE) in response tothe control signal V_(CS). The LED driver 104 may be configured tocontrol the power delivered to the LED light source 106, for example, byregulating the voltage generated across the LED light source 106 and/orregulating the current conducted through the LED light source 106.Examples of an LED driver are described in greater detail incommonly-assigned U.S. Pat. No. 8,492,987, issued Jul. 23, 2013,entitled LOAD CONTROL DEVICE FOR A LIGHT-EMITTING DIODE LIGHT SOURCE,and U.S. Pat. No. 9,232,574, issued Jan. 5, 2016, entitled FORWARDCONVERTER HAVING A PRIMARY-SIDE CURRENT SENSE CIRCUIT, the entiredisclosures of which are hereby incorporated by reference. Althoughdescribed as an LED light source driven by an LED driver, the electricalload referenced herein may comprise an electronic ballast for driving afluorescent lamp.

The load control device 100 may comprise a switching circuit 110, whichmay be electrically coupled in series between the hot terminal H and theswitched hot terminal SH. The switching circuit 110 may be renderedconductive and non-conductive in response to actuations of an on/offactuator 112 (e.g., a toggle switch) to generate a switched-hot voltageV_(SH) at the switched hot terminal SH. The on/off actuator 112 maycomprise a mechanical switch that is actuated by a slider control, forexample, when the slider control reaches a minimum position (e.g., a“slide-to-off” slider control).

The load control device 100 may also include a driver communicationcircuit 114 that may comprise a current sink circuit adapted to sinkcurrent from the LED driver 104 via the control wiring 108. The LEDdriver 104 may be configured to generate a link supply voltage (e.g.,approximately 10 V) to allow the current sink circuit of the drivercommunication circuit 114 to generate the control signal V_(CS) on thecontrol wiring 108. The load control device 100 may comprise a powersupply 116 coupled between the hot terminal H and the neutral terminal Nfor generating a DC supply voltage V_(CC) for powering the low-voltagecircuitry of the load control device 100.

The load control device 100 may comprise a control circuit 120 (e.g., adigital control circuit) configured to control the driver communicationcircuit 114 to generate the control signal V_(CS) for adjusting theintensity of the LED light source 106. The control circuit 120 mayinclude a microprocessor 122. The control circuit 120 could also includeany suitable controller or processing device, such as, for example, aprogrammable logic device (PLD), a microcontroller, an applicationspecific integrated circuit (ASIC), or a field programmable gate array(FPGA). The microprocessor 122 may be configured to determine a desiredlight intensity L_(DES) for the LED light source 106 and a correspondingdesired magnitude V_(DES) for the control signal V_(CS) in response toan intensity adjustment actuator 124 (e.g., a slider control). Forexample, the microprocessor 122 may be configured to receive a DCpotentiometer wiper voltage V_(POT) from a potentiometer circuit 126,which may be responsive to the intensity adjustment actuator 124. Themicroprocessor 122 may be configured to control the magnitude of thecontrol signal V_(CS) to the desired magnitude V_(DES) so as to adjustthe intensity of the LED light source 106 to the desired light intensityL_(DES) (e.g., between a low-end intensity L_(LE) and a high-endintensity L_(HE)).

The microprocessor 122 of the control circuit 120 may generate adirect-current (DC) output signal V_(DC) and provide the output signalV_(DC) to the driver communication circuit 114. For example, themicroprocessor 122 may comprise a digital-to-analog converter (DAC) forgenerating the DC output signal V_(DC) that is received by the drivercommunication circuit 114 for generating the control signal V_(CS). Themicroprocessor 122 may adjust the magnitude of the control signal V_(CS)by adjusting the magnitude of the output signal V_(DC). The outputsignal V_(DC) may comprise a pulse-width modulated (PWM) signal orvariable-frequency waveform, in response to which the drivercommunication circuit 114 may be configured to adjust the magnitude ofthe control signal V_(CS). The driver communication circuit 114 maycomprise a current source circuit or a current source/sink circuit forgenerating the control signal V_(CS) in response to the output signalV_(DC).

The LED driver 104 may be controlled to an electronic off (e.g.,standby) state during which the LED driver 104 may turn off the LEDlight source while control circuitry of the LED driver remains powered.The LED driver 104 may be configured to change between an on state andthe electronic off state in response to the control signal V_(CS) (e.g.,using hysteresis). For example, during the on state, the control circuit120 may be configured to adjust the DC voltage level of the controlsignal V_(CS) between a low-end magnitude V_(LE) (e.g., approximately0.9 volts) and a high-end magnitude V_(HE) (e.g., ten volts) to adjustthe intensity of the LED light source 106 between the low-end intensityL_(LE) and the high-end intensity L_(HE), respectively. To control theLED driver 104 into the electronic off state, the control circuit 120may be configured to adjust the DC voltage level of the control signalV_(CS) to a standby level. For example, the LED driver 104 may beconfigured to change to the electronic off state when the DC voltagelevel of the 0-10V control signal drops below a falling thresholdV_(TH-FALLING) (e.g., approximately 0.6 V). The LED driver 104 may beconfigured to return to the on state (e.g., to turn on) when the DCvoltage level of the control signal V_(CS) rises above a risingthreshold V_(TH-RISING) (e.g., approximately 1.0 V), after which the LEDdriver 104 may adjust the intensity of the LED light source 106 betweenthe low-end intensity L_(LE) and the high-end intensity L_(HE) as thecontrol signal V_(CS) ranges between the low-end magnitude V_(LE) andthe high-end magnitude V_(HE).

During the on state, the low-end magnitude V_(LE) of the control signalV_(CS) may be less than the rising threshold V_(TH-RISING). For example,the low-end magnitude V_(LE) of the control signal V_(CS) may beapproximately 0.9 V while the rising threshold V_(TH-RISING) may beapproximately 1.0 V. If the LED driver 104 and the load control device100 temporarily lose power while the load control device is controllingthe intensity of the LED light source 106 to the low-end intensityL_(LE), the magnitude of the control signal V_(CS) (e.g., the low-endmagnitude V_(LE)) may not exceed the rising threshold V_(TH-RISING) whenpower is restored and the LED driver 104 may not turn on the LED lightsource 106. Similarly, when the on/off actuator 112 is actuated to closethe switching circuit 110 to turn the LED light source 106 on and theintensity adjustment actuator 122 is set to the low-end intensityL_(LE), the magnitude of the control signal V_(CS) may also not exceedthe rising threshold V_(TH-RISING) and the LED driver 104 may not turnon the LED light source 106 when the LED driver 104 is switched on bythe switching circuit 110.

Accordingly, the control circuit 120 may be configured to at leasttemporarily increase the magnitude of the control signal V_(CS) whenpower is applied (e.g., initially applied or re-applied) to the lightingload 106 (i.e., to the LED driver 104). For example, the control circuit120 may be configured to temporarily increase the magnitude of thecontrol signal V_(CS) to be equal to or above the rising thresholdV_(TH-RISING) when power is applied to the LED driver after aninterruption and the desired magnitude V_(DES) for the control signalV_(CS) is initially less than the rising threshold V_(TH-RISING). Thepower interruption may be caused by a power outage or a manualswitch-off of the on/off actuator 112, for example. The control circuit120 may comprise a voltage sense circuit 128 configured to generate avoltage sense signal V_(SENSE) that may indicate when power has beenapplied to the LED driver 104. For example, the voltage sense circuit128 may be coupled between the switched hot terminal SH and the neutralterminal N to receive the switched-hot voltage V_(SH) as shown inFIG. 1. The voltage sense circuit 128 may be configured to drive thevoltage sense signal V_(SENSE) high towards the supply voltage V_(CC)when the magnitude of the switched-hot voltage V_(SH) rises above avoltage sense threshold V_(TH-SENSE) (e.g., the voltage sense circuit128 may comprise a comparator circuit). In an example, the controlcircuit 120 may be configured to determine that power has just beenapplied to the LED driver 104 in response to detecting a rising edge ofthe voltage sense signal V_(SENSE). In another example, the voltagesense signal V_(SENSE) may simply be a scaled version of theswitched-hot voltage V_(SH) (e.g., the voltage sense circuit 128 maycomprise a scaling circuit, such as a resistive divider), and thecontrol circuit 120 may be configured to sample the voltage sense signalV_(SENSE) and compare the sampled magnitude to the voltage sensethreshold V_(TH-SENSE) to determine when power has just been applied (orre-applied) to the LED driver 104.

While the switching circuit 110 and the on/off actuator 112 is shown inFIG. 1 as integral with the load control device 100, the switchingcircuit and/or the on/off actuator 112 could be external to the loadcontrol device 100 (e.g., the switching circuit could be included in anexternal light switch or an external switching power pack). In addition,the switching circuit 110 could comprise a relay controlled by themicroprocessor 122 and the on/off actuator 112 could comprise alow-voltage switch (e.g., a mechanical tactile switch) for generating alow-voltage signal that is received by the microprocessor 122. Themicroprocessor 122 may be configured to detect that the low-voltageswitch has been actuated, close the relay, and temporarily increase themagnitude of the control signal V_(CS) (e.g., without the need for thevoltage sense circuit 128).

As described herein, power being applied (e.g., initially applied orre-applied) to the lighting load 106 may occur when power is restoredafter a temporary power interruption (e.g., by an electrical utilitycompany), when the switching circuit 110 is closed, and/or when anexternal switching circuit (e.g., in a light switch or a switching powerpack) coupled in series between the AC power source 102 and the lightingload 106 is closed. One of ordinary skill in the art will recognize thatthere are other ways that power may be applied to a lighting load.

FIG. 2 is a simplified flowchart of a voltage sense procedure 200 thatmay be executed by the microprocessor 122 of the control circuit 120 ofthe load control device 100. FIG. 3 is a simplified diagram of examplewaveforms illustrating the operation of the load control device 100during the voltage sense procedure 200. The voltage sense procedure 200may begin when the microprocessor 122 detects a rising edge of thevoltage sense signal V_(SENSE) at step 210 indicating that power hasjust been applied to the LED driver 104 (e.g., as shown at timet_(RISING) in FIG. 3), e.g., after an interruption. The microprocessor122 may then determine the desired magnitude V_(DES) for the controlsignal V_(CS) (e.g., using the desired light intensity L_(DES)determined from the intensity adjustment actuator 122) at step 212. Ifthe desired magnitude V_(DES) is not less than the rising thresholdV_(TH-RISING) at step 214, the microprocessor 122 may set the magnitudeof the control signal V_(CS) to the desired magnitude V_(DES) at step216, before the voltage sense procedure 200 exits. If the desiredmagnitude V_(DES) is less than the rising threshold V_(TH-RISING) atstep 214, the microprocessor 122 may set the magnitude of the controlsignal V_(CS) to be equal to the rising threshold V_(TH-RISING) plus anoffset voltage V_(OFFSET) at step 218. For example, the offset voltageV_(OFFSET) may be sized to ensure that the magnitude of the controlsignal V_(CS) is greater than the rising threshold V_(TH-RISING) whenpower is applied to the LED driver 104 (e.g., as shown at timet_(RISING) in FIG. 3) so as to drive the LED driver 104 to the on state.The microprocessor 122 may then fade (e.g., adjust) the magnitude of thecontrol signal V_(CS) to the desired magnitude V_(DES) (e.g., thelow-end magnitude V_(LE) as shown in FIG. 3) over a first period of timeT_(FADE), which may be approximately 0.5-1 second, at step 220, beforethe voltage sense procedure 200 exits. While not shown in FIG. 2, themicroprocessor 122 may hold the magnitude of the control signal V_(CS)equal to the rising threshold V_(TH-RISING) plus the offset voltageV_(OFFSET) for a second period of time before beginning to fade themagnitude of the control signal V_(CS) to the desired magnitude V_(DES)over the period of time T_(FADE).

The operation of the control circuit 120 in response to the applicationof power to the LED driver 104 may be controllable and/or programmable.For example, the control circuit 120 may be configured to adjust themagnitude of the offset voltage V_(OFFSET), and/or the length of thefirst and/or the second time period (e.g., the period of time T_(FADE)),in response to an external input (e.g., a programming input). Theexternal input may be received, for example, from an actuation of theintensity adjustment actuator 124 and/or the on/off actuator 112, anactuation of one or more programming buttons (not shown), an actuationof one or more separate programming potentiometers (not shown), and/orone or more messages received via a communication circuit (not shown).

FIG. 4 is a simplified block diagram of another example of a 0-10V loadcontrol device 300. The load control device 300 may be configured tocontrol an amount of power delivered to an electrical load. Theelectrical load may include, e.g., a load regulation circuit for drivingthe electrical load, such as an LED driver 304 for controlling an LEDlight source 306. The load control device 300 may or may not beelectrically coupled in series between an AC power source 302 and theelectrical load. The load control device 300 may comprise first andsecond control terminals C1, C2 adapted to be coupled to the LED driver304 via a control wiring 308. The load control device 300 may comprise acommunication circuit configured to generate a control signal forcontrolling power delivered to the LED lighting load 306. The loadcontrol device 300 may include, for example, a current sink circuit 310electrically coupled to the control terminals C1, C2 for sinking currentfrom the LED driver 104 via the control wiring 108. The current sinkcircuit 310 may be configured to generate a DC control signal V_(CS) forcontrolling the LED driver 304 to turn the LED light source 306 on andoff, and to adjust the intensity of the LED light source 306 when theLED light source 306 is on.

The load control device 300 may comprise a control circuit 320 (e.g., ananalog control circuit) configured to control the current sink circuit310 to generate the control signal V_(CS) for turning the LED lightsource 306 on and off, and for adjusting the intensity of the LED lightsource 306. The control circuit 320 may comprise a potentiometer circuit322 for generating a DC output signal V_(DC) in response to an intensityadjustment actuator 324 (such as, e.g., a slider control, a thumbwheel,or a knob). The potentiometer circuit 322 may provide the DC outputsignal V_(DC) to the current sink circuit 310 for controlling themagnitude of the control signal V_(CS) to a desired magnitude V_(DES) soas to adjust the intensity of the LED light source 306 to a desiredlight intensity L_(DES) (e.g., between a low-end intensity L_(LE) and ahigh-end intensity L_(HE)).

The LED driver 304 may be controlled to an electronic off (e.g.,standby) state during which the LED driver 304 may turn off the LEDlight source while control circuitry of the LED driver remains powered(e.g., in a similar manner as the LED driver 104 shown in FIG. 1). TheLED driver 304 may be configured to change between an on state and theelectronic off state in response to the control signal V_(CS) (e.g.,using hysteresis). For example, the LED driver 304 may be configured tochange to the on state (i.e., to turn on) when the DC voltage level ofthe control signal V_(CS) rises above a rising threshold V_(TH-RISING)(e.g., approximately 1.0 V).

As with the load control device 100 of FIG. 1, the low-end magnitudeV_(LE) of the control signal V_(CS) generated by the load control device300 may be less than the rising threshold V_(TH-RISING). In some cases(such as, e.g., when a desired magnitude of the control signal V_(CS) isless than the rising threshold V_(TH-RISING) when power is applied tothe LED light source 306), the control circuit 320 may be configured totemporarily increase the magnitude of the control signal V_(CS) to beequal to or greater than the rising threshold V_(TH-RISING) beforedecreasing the magnitude of the control signal V_(CS) to the desiredmagnitude. The control circuit 320 may be configured to determine whenpower is applied to the LED light source 306 (e.g., to the LED driver304) in response to the magnitude (e.g., a change of the magnitude) ofthe control signal V_(CS) generated by the current sink circuit 310. Forexample, the LED driver 304 may be configured to generate a link supplyvoltage to allow the current sink circuit 310 to generate the controlsignal V_(CS) on the control wiring 308. As such, the magnitude of thecontrol signal V_(CS) may indicate when the LED driver 304 is powered.For example, when the LED driver 304 is unpowered, the magnitude of thecontrol signal V_(CS) may drop to approximately zero volts. When poweris restored, the magnitude of the control signal V_(CS) may rise back tothe level before power was lost. The control circuit 320 may beconfigured to determine that power has been lost and re-applied based onthe changes (e.g., the drop and rise) in the magnitude of the controlsignal V_(CS).

The control circuit 320 may comprise a bump-up circuit 330 fortemporarily increasing the magnitude of the control signal V_(CS) (e.g.,when power is applied to the LED driver 304). FIG. 5 is a simplifieddiagram of example waveforms illustrating the operation of the bump-upcircuit 330 of the load control device 300. The bump-up circuit 330 maycomprise a bipolar junction transistor Q332 that may in turn include acollector coupled to an anode of a capacitor C334, the seriescombination of which is coupled between the first control terminal C1and the wiper of the potentiometer circuit 322 (e.g., the DC outputsignal V_(DC) of the control circuit 320), with an emitter of thetransistor Q332 coupled to the first control terminal C1, and a cathodeof the capacitor C334 coupled to the wiper of the potentiometer circuit322 and the current sink circuit 310. The bump-up circuit 330 mayfurther comprise two resistors R336, R338 coupled in series between thefirst and second control terminals C1, C2. The tie point of theresistors R336, R338 may be coupled to the base of the transistor Q332.

When the magnitude of the control signal V_(CS) is approximately zerovolts (e.g., the LED driver 304 is unpowered), the transistor Q332 maybe non-conductive and the capacitor C334 may be uncharged. After poweris applied to the LED driver 304, the LED driver 304 may begin togenerate the link supply voltage (e.g., across the resistors R334, R336of the bump-up circuit 330). Once the voltage across the resistor R334exceeds the rated emitter-base voltage of the transistor Q332, thetransistor may become conductive. When the transistor Q332 first becomesconductive, the capacitor C334 may be uncharged, and thus the transistorQ332 may pull the magnitude of the DC output signal V_(DC) up towardsthe magnitude at the first control terminal C1. This may cause thecurrent sink circuit 310 to temporarily increase the magnitude of thecontrol signal V_(CS) to be greater than the rising thresholdV_(TH-RISING) (e.g., by an offset voltage V_(OFFSET)). As the capacitorC334 charges, the magnitude of the DC output signal V_(DC) may continueto fall until the capacitor C334 is fully charged and the magnitude ofthe DC output signal V_(DC) has returned to the level determined by thepotentiometer circuit 322 and the intensity adjustment actuator 324(e.g., the low-end magnitude V_(LE) as shown in FIG. 5). The bump-upcircuit 330 may be configured to temporarily increase the magnitude ofthe control signal V_(CS) for a bump-up period T_(BUMP) (e.g., as shownin FIG. 5).

What is claimed is:
 1. A load control device for controlling an amountof power delivered to a lighting load, the load control devicecomprising: a communication circuit configured to generate a controlsignal for controlling the amount of power delivered to the lightingload, the control signal being capable of causing the lighting load tobe turned on when a magnitude of the control signal rises above athreshold; and a control circuit configured to control the communicationcircuit to adjust the magnitude of the control signal so as to adjust anintensity of the lighting load between a low-end intensity and ahigh-end intensity, the control signal having a magnitude less than thethreshold when the intensity of the lighting load is being controlled tothe low-end intensity; wherein, when power has been applied to thelighting load, the control circuit is further configured to: determinethat a desired magnitude of the control signal is below the threshold;and set the magnitude of the control signal to be equal to or greaterthan the threshold before decreasing the magnitude of the control signalto the desired magnitude.
 2. The load control device of claim 1, furthercomprising: an intensity adjustment actuator; wherein the controlcircuit comprises a potentiometer circuit responsive to the intensityadjustment actuator for determining the desired magnitude of the controlsignal.
 3. The load control device of claim 2, wherein the controlcircuit comprises a digital control circuit configured to control thecommunication circuit to set the magnitude of the control signal to beequal to or greater than the threshold when power has been applied tothe lighting load, and decrease the magnitude of the control signal tothe desired magnitude over a first period of time.
 4. The load controldevice of claim 3, wherein the control circuit is configured to maintainthe magnitude of the control signal constant at a level equal to orgreater than the threshold for a second period of time when power hasbeen applied to the lighting load before decreasing the magnitude of thecontrol signal to the desired magnitude over the first period of time.5. The load control device of claim 3, further comprising: a sensecircuit configured to provide an indication of when power has beenapplied to the lighting load.
 6. The load control device of claim 2,wherein the control circuit comprises an analog control circuit thatincludes a bump-up circuit coupled to a wiper of the potentiometercircuit for increasing the magnitude of the control signal.
 7. The loadcontrol device of claim 1, wherein the communication circuit comprises acurrent sink circuit.
 8. A method implemented in a load control devicefor controlling a lighting load, the method comprising: generating acontrol signal for controlling an amount of power delivered to thelighting load, the control signal being capable of causing the lightingload to be turned on when a magnitude of the control signal rises abovea threshold; adjusting, after the lighting load has been turned on, themagnitude of the control signal so as to control an intensity of thelighting load between a low-end intensity and a high-end intensity, themagnitude of the control signal being equal to or less than thethreshold when the intensity of the lighting load is being controlled tothe low-end intensity; determining, when power has been applied to thelighting load, that a desired magnitude of the control signal is belowthe threshold; and setting the magnitude of the control signal to beequal to or greater than the threshold before decreasing the magnitudeof the control signal to the desired magnitude.
 9. The method of claim8, further comprising: sensing, via a sense circuit, that power has beenapplied to the lighting load.
 10. The method of claim 8, wherein themagnitude of the control signal is set to be equal to or greater thanthe threshold via a bump-up circuit coupled to a wiper of apotentiometer.
 11. The method of claim 8, wherein the magnitude of thecontrol signal is set equal to or greater than the threshold via digitalcontrol circuit.
 12. The method of claim 8, wherein the magnitude of thecontrol signal is decreased to the desired magnitude over a first periodof time.
 13. The method of claim 12, wherein the magnitude of thecontrol signal is maintained at a level equal to or greater than thethreshold for a second period of time before being decreased to thedesired magnitude over the first period of time.
 14. A load controldevice for controlling an amount of power delivered to a lighting load,the load control device comprising: a control circuit configured toadjust a magnitude of a control signal to control the amount of powerdelivered to the lighting load, the control signal being capable ofcausing the lighting load to be turned on when the magnitude of thecontrol signal rises above a threshold, wherein the control circuit isfurther configured to: when the lighting load is in an on state, adjustthe magnitude of the control signal to control an intensity of thelighting load between a low-end intensity and a high-end intensity, themagnitude of the control signal being less than the threshold when theintensity of the lighting load is at the low-end intensity; and when thelighting load is in an off state: determine that power has been appliedto the lighting load; determine that a desired magnitude of the controlsignal is below the threshold; and set the magnitude of the controlsignal to be greater than the threshold by an offset amount to turn onthe lighting load.
 15. The load control device of claim 14, wherein thecontrol circuit is further configured to decrease the magnitude of thecontrol signal to the desired magnitude over a first period of time. 16.The load control device of claim 15, wherein the control circuit isconfigured to maintain the magnitude of the control signal above thethreshold for a second period of time before decreasing the magnitude ofthe control signal to the desired magnitude over the first period oftime.
 17. The load control device of claim 16, wherein the controlcircuit is further configured to adjust the respective values of theoffset amount, the first period of time, and the second period of timebased on an external input.
 18. The load control device of claim 14,wherein the load control device is connected to a power source thatpowers the lighting load, the load control device further comprising: asense circuit configured to sense that power has been applied to thelighting load.
 19. The load control device of claim 14, furthercomprising: a current sink circuit configured to generate the controlsignal by sinking current through a load regulation device that iscontrolling the lighting load.
 20. The load control device of claim 19,wherein the control circuit is further configured to determine thatpower has been applied to the lighting load based on a change in themagnitude of the control signal.
 21. The load control device of claim20, wherein the change in the magnitude of the control signal includesan increase of the magnitude of the control signal from approximatelyzero volts to the desired magnitude.